The invention relates to color photosensitive elements, and more particularly to color photosensitive elements which function on the principle of position/transit time vs. color to obtain color separations.
Monochrome image sensor arrays typically comprise an array of photosensitive elements which scan an image bearing document and convert the microscopic image area viewed by each photosensitive element to image signal charges or pixels. To implement a full color array for the above application requires the use of more elaborate sensor arrays. Typically, two implementations have been used for full color sensing. One implementation is to use a monochrome sensor array as described above and place color filters, for instance red, green, blue for full color, on the photosensitive elements in an alternating manner. The three photosensitive elements would represent one color pixel. Even though full color images are produced, the resolution of the scan has been decreased by one third and further, each resulting pixel contains information for only one color instead of all three colors as is desirable. A second implementation involves the use of three linear arrays, each array having a color filter, and positioning the three arrays in parallel, one disposed above the other. The resolution is preserved but as the sensor arrays scan the page, memory would be required to delay the color information from two of the arrays to provide full color information for any one pixel. Memory requirements of this magnitude can be expensive to implement and also consume valuable space. In addition, the higher data rate required to transmit and process multicolor images at speeds of one full page per second or higher can exceed band width capabilities of conventional silicon (Si) image sensor arrays, also requiring the use of parallel input channels and logic array components.
U.S. Pat. No. 4,847,489 to Dietrich discloses a GaAs color CCD arrangement using a multilayer structure of alternating positively and negatively doped photosensitive materials. To control light sensitivity, the system uses different applied voltages to different layers of the device. U.S. Pat. No. 4,613,895 to Burkey et al. discloses a color sensor utilizing depth dependent absorption of light. The structure involves alternately doped layers of the same semiconductor using Si as the photoactive element. U.S. Pat. No. 4,695,859 to Guha et al. discloses a monochrome multilayer thin film light emitting and detecting array. The multiple layers provide a panchromatic response for the emitter of the device. U.S. Pat. No. 4,301,463 to Burrus, Jr. et al., U.S. Pat. No. 4,213,138 to Campbell et al. and Xerox Disclosure Journal, Volume 11 Number 3, dated May/June 1986 titled "Wavelength Demultiplexing Detector" disclose a three terminal demultiplexing photodiode wherein information present simultaneously at two distinct wavelengths can be developed into two currents. U.S. Pat. No. 4,696,533 to Kingston et al. discloses a spatial light modulator which uses a substrate having a buried channel CCD formed therein, wherein the amount of charge in the charge storage well associated with the electrode of the CCD is controlled by an electrically or optically addressed data signal. The modulator uses an electric field to shift the absorption of light. U.S. Pat. No. 4,496,981 to Ota discloses a color video camera system using three pixels, one each for the red, green and blue separations to provide information for one color pixel. U.S. Pat. No. 4,984,032 to Miura et al. discloses an avalanche photodiode wherein a light to be detected is injected through a substrate via an opening in the substrate electrode, while producing no carriers therein, into the light absorption layer.
U.S. Pat. No. 4,117,510 to Ohta et al., U.S. Pat. No. 4,500,915 to Koike et al., U.S. Pat. No. 4,656,503 to Hynecek, U.S. Pat. No. 4,663,535 to Nakai et al., and U.S. Pat. No. 4,709,259 to Suzuki et al. disclose transistor arrays in two dimensions along with color filters to differentiate colors. U.S. Pat. No. 4,264,915 to Bierhenke et al., U.S. Pat. No. 4,814,836 to Thompson, U.S. Pat. No. 4,814,847 to Tabatabaie, U.S. Pat. No. 4,840,446 to Nakamura et al., U.S. Pat. No. 4,860,066 to Kirchner et al., U.S. Pat. No. 4,873,555 to Coon et al. U.S. Pat. No. 4,604,527 to Chenevas-Paule et al. and U.S. Pat. No. 4,644,402 to Yamada disclose group III-V compound sensors which also require spatially separate photosensitive elements for different colors.